Method for forming a protective coating film on electronic parts and devices

ABSTRACT

Proposed is a novel method for the formation of a protective coating film having a pencil hardness of up to 9 H on the surface of various substrates or, in particular, electronic parts such as color filters and liquid crystal display panels. The method comprises: coating the surface with a liquid coating composition of which the principal ingredient is a partial cohydrolysis-condensation product of a tetraalkoxy silane, e.g., tetraethoxy silane, and a functional alkoxy silane, e.g., 3-methacryloxypropyl trimethoxy silane, and drying and heating the coating layer to effect complete curing. The hardness of the cured protective film can be increased by admixing the liquid coating composition with a finely divided inorganic filler such as a colloidal silica. It is optional that the functional alkoxy silane is subjected to the cohydrolysis reaction after it is polymerized alone or after it is copolymerized with a polyfunctional acrylic monomer.

BACKGROUND OF THE INVENTION

The present invention relates to a method for the formation of aprotective coating film on the surface of a substrate material. Moreparticularly, the invention relates to a method for the formation of auniform protective coating film having a very high hardness on thesurface of various kinds of substrates such as electronic parts anddevices.

As is well known, the surface of various kinds of electric andelectronic parts such as liquid-crystal display panels and the like isrequired to be protected against scratches and other mechanical damagesby forming a protective coating film thereon having high hardness.

Liquid-crystal display panels usually have a structure consisting of twosubstrate plates made from a transparent material such as glass, acrylicresins, polyethylene terephthalate resins and the like held in parallelwith a narrow gap space therebetween, which is filled with a liquidcrystal substance, the peripheries of the parallel plates beingair-tightly sealed with a glass frit or an organic sealant. Each of thetwo parallel plates is provided on the inwardly facing surface with apattern of electrodes while an orientation membrane is formed on theareas in contact with the liquid crystal substance which serves to alignthe liquid crystal molecules in a definite direction when an electricvoltage is applied to the electrodes. Such an orientation membrane isprepared by forming a coating layer of an organic synthetic resin on thesurface of each of the substrate plates having the electrodes followedby rubbing the surface in a definite direction with a cotton cloth andthe like, i.e. a so-called rubbing treatment.

In the above described manufacturing procedure of liquid crystal displaypanels, however, a trouble is sometimes unavoidable that cracks areformed in the electrodes under the influences of mechanical forces. Thisis presumably a consequence of the difference in the thermal expansioncoefficients which is not negligible between the orientation membranemade from an organic material and the electrodes made from an inorganicmaterial of high hardness such as ITO and the like.

With an object to solve the above mentioned problems, a method isproposed according to which a protective coating film mainly consistingof silicon dioxide is interposed between the electrodes and theorientation membrane. Such a silicon dioxide-based intermediate film canbe prepared by coating the substrate surface with a liquid coatingcomposition containing a silanol compound followed by baking of thecoating layer while such a baking treatment causes another problem thatdegradation is caused in the electrodes to increase the electricresistivity thereof because the baking temperature must be as high as400° C. or even higher.

In recent years, moreover, so-called plastic liquid crystal displaypanels have been developed, of which the substrates are made from asynthetic resin such as acrylic resins, poly(ethylene terephthalate)resins and the like. It is important in such a plastic liquid crystaldisplay panel that the electrodes are provided with a protective filmhaving a high hardness and capable of being formed by baking at arelatively low baking temperature because the plastic substrates arethermally not stable enough at an elevated temperature.

Another important objective in the electronic industry, of which ahigh-hardness protective film is desired to be formed on the surface, isa color filter which is a transparency colored pattern-wise mainly inthree primary colors of red, blue and green and used by mounting on thesubstrate plate of a color display device such as a liquid crystal colordisplay panel. In the preparation of such a color display device, thepreparation of the color filter is followed, usually, by the formationof a transparent electroconductive film and an orientation membrane.

Troubles are sometimes unavoidable in this procedure that creases andcracks are formed in the colored coating film of the color filter orfissures are formed in the electroconductive film. These troubles arecaused as a consequence of the larger than negligible difference in thethermal expansion coefficients between the colored coating film, whichis made from an organic material such as dyes, organic pigments,synthetic resins and the like, and the transparent electroconductivefilm made from an inorganic material of high hardness such as ITO andthe like.

Various proposals have been made heretofore to solve the above mentionedproblems, for example, by providing a protective film on the coloredcoating film of the color filter. Examples of such a protective filminclude those formed by coating the surface with a solution prepared bydissolving a solvent-soluble polyamide resin or a polyimide resin in alactone compound, a phenol compound or a mixture thereof as the solventfollowed by drying as disclosed in Japanese Patent Kokai 62-163016,those consisting mainly of silicon dioxide as disclosed in JapanesePatent Kokai 62-242918 and those consisting of an overcoating layer of athermosetting resin which can retain transparency by curing, of whichthe temperature for the exothermic peak in the crosslinking and curingreaction is 200° C. or higher as is disclosed in Japanese Patent Kokai63-131103. These protective films heretofore proposed, however, are notquite satisfactory in respects of the heat resistance, light fastness,hardness, adhesion and stability against sputtering so that it iseagerly desired to develop a method for forming a protective film on acolor filter, of which high precision is essential, without problems dueto the above mentioned deficiencies in the prior art methods usingconventional coating agents.

SUMMARY OF THE INVENTION

The present invention accordingly has an object to provide a novel andimproved method for the formation of a protective coating film on thesurface of various kinds of electronic parts and devices includingliquid crystal display panels and color filters, which method is freefrom the above described problems and disadvantages in the prior artmethods and can be performed in a remarkably simple and convenientprocedure including a relatively low baking temperature.

Thus, the method of the present invention for the formation of aprotective coating film on the surface of a substrate comprises thesteps of:

(a) coating the surface with a liquid coating composition containing, asthe principal ingredient, a partial cohydrolysis-condensation product ofa first silane compound represented by the general formula

    Si(OR).sub.4,                                              (I)

in which R is an alkyl group having 1 to 4 carbon atoms or a phenylgroup, and a second silane compound represented by the general formula

    R.sup.1.sub.n Si(OR).sub.4-n,                              (II)

in which R has the same meaning as defined above, R¹ is a functionalgroup which is a polymerizable group selected from the class consistingof vinyl group, 3-acryloxypropyl group and 3-methacryloxypropyl group ora 3-glycidyloxypropyl group and the subscript n is 1, 2 or 3, to form acoating layer on the surface; and

(b) drying and heating the coating layer at a temperature in the rangefrom 140° to 300° C. for 15 to 120 minutes to effect curing of the driedcoating layer.

Though optional, the liquid coating composition used in step (a) of theinventive method is admixed with an inorganic filler having an averageparticle diameter in the range from 5 to 200 nm in order to enhance themechanical strengths of the protective coating film formed by theinventive method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is described above, the inventive method comprises the steps ofcoating the surface of the substrate with a specific liquid coatingcomposition, of which the principal ingredient is a partialcohydrolysis-condensation product of two different kinds of silanecompounds to form a coating layer and drying and heating the thus formedcoating layer under specified heating conditions to effect curing of thecoating layer.

The first silane compound to be subjected to the partialcohydrolysis-condensation reaction with the second silane compound isrepresented by the above given general formula (I), in which the groupdenoted by R is an alkyl group having 1 to 4 carbon atoms or a phenylgroup. Particular examples of the first silane compound includetetramethoxy silane, tetraethoxy silane, tetrapropoxy silane,tetrabutoxy silane and tetraphenoxy silane, of which tetramethoxy silaneand tetraethoxy silane are preferred.

On the other hand, the second silane compound to be subjected to thepartial cohydrolysis-condensation reaction with the above mentionedfirst silane compound is represented by the general formula (II), inwhich the subscript n is 1, 2 or 3, R has the same meaning as definedfor the first silane compound and R¹ is a functional group which is apolymerizable group selected from the class consisting of a vinyl group,3-acryloxypropyl group and 3-methacryloxypropyl group or a3-glycidyloxypropyl group.

Particular examples of the second silane compound in conformity with thedefinition of the general formula (II) include:

3-acryloxypropyl trimethoxy silane, 3-methacryloxypropyl trimethoxysilane, 3-glycidyloxypropyl trimethoxy silane, vinyl trimethoxy silane,di(3-acryloxypropyl) dimethoxy silane, di(3-methacryloxypropyl)dimethoxy silane, di(3-glycidyloxypropyl) dimethoxy silane, divinyldimethoxy silane, tri(3-acryloxypropyl) methoxy silane,tri(3-methacryloxypropyl) methoxy silane, tri(3-glycidyloxypropyl)methoxy silane, trivinyl methoxy silane, 3-acryloxypropyl triethoxysilane, 3-methacryloxypropyl triethoxy silane, 3-glycidyloxypropyltriethoxy silane, vinyl triethoxy silane, di(3-acryloxypropyl) diethoxysilane, di(3-methacryloxypropyl) diethoxy silane,di(3-glycidyloxypropyl) diethoxy silane, divinyl diethoxy silane,tri(3-acryloxypropyl) ethoxy silane, tri(3-methacryloxypropyl) ethoxysilane, tri(3-glycidyloxypropyl) ethoxy silane, trivinyl ethoxy silane,3-acryloxypropyl tripropoxy silane, 3-methacryloxypropyl tripropoxysilane, 3-glycidyloxypropyl tripropoxy silane, vinyl tripropoxy silane,di(3-acryloxypropyl) dipropoxy silane, di(3-methacryloxypropyl)dipropoxy silane, di(3-glycidyloxypropyl) dipropoxy silane, divinyldipropoxy silane, tri(3-acryloxypropyl) propoxy silane,tri(3-methacryloxypropyl) propoxy silane, tri(3-glycidyloxypropyl)propoxy silane, trivinyl propoxy silane, 3-acryloxypropyl tributoxysilane, 3-methacryloxypropyl tributoxy silane, 3-glycidyloxypropyltributoxy silane, vinyl tributoxy silane, di(3-acryloxypropyl) dibutoxysilane, di(3-methacryloxypropyl) dibutoxy silane,di(3-glycidyloxypropyl) dibutoxy silane, divinyl dibutoxy silane,tri(3-acryloxypropyl) butoxy silane, tri(3-methacryloxypropyl) butoxysilane, tri(3-glycidyloxypropyl) butoxy silane, trivinyl butoxy silaneand the like.

The liquid coating composition used in the method of the invention canbe prepared by adding the above described first and second silanecompounds in a suitable proportion into an organic solvent to form asolution which is then admixed with an appropriate amount of water and asmall amount of an acid such as hydrochloric acid as a catalyst forpromoting the reactions of hydrolysis and condensation of the silanecompounds to obtain a partial cohydrolysis-condensation product of thesilane compounds. It is further optional that the first and the secondsilanes are partially hydrolyzed separately beforehand and the thusobtained partial hydrolysis-condensation products are mixed together inan appropriate proportion, if they are compatible with each other, togive a liquid coating composition.

Examples of organic solvents suitable as a diluent of the silanecompounds in the partial cohydrolysis-condensation reaction thereofinclude monohydric alcohols such as methyl, ethyl, propyl and butylalcohols; polyhydric alcohols such as ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, hexylene glycol andoctylene glycol; ethers such as ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monopropyl ether,ethylene glycol monobutyl ether, propylene glycol monomethyl ether,propylene glycol monoethyl ether, propylene glycol monopropyl ether,ethylene glycol dimethyl ether, ethylene glycol diethyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol dimethyl ether, diethylene glycol diethyl ether,propylene glycol dimethyl ether, propylene glycol diethyl ether,dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether,dipropylene glycol dimethyl ether and dipropylene glycol diethyl ether;fatty acids such as acetic acid and propionic acid; and esters such asmethyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butylacetate, isobutyl acetate, methyl propionate and ethyl propionate.

It is optional that the liquid coating composition used in the inventivemethod is admixed with a small amount of a polyfunctional acrylicmonomer exemplified by pentaerythritol triacrylate, pentaerythritoltrimethacrylate, pentaerythritol tetraacrylate, pentaerythritoltetramethacrylate, dipentaerythritol hexaacrylate, dipentaerythritolhexamethacrylate, dipentaerythritol pentaacrylate,hexa(2-methacryloxyethoxy) phosphazene, tris(2-acryloxyethyl)isocyanurate and tris(2-methacryloxyethyl) isocyanurate and the like.

When the viscosity of the liquid coating composition used in theinventive method as prepared in the above described manner is too highto be applied to the substrate surface by a conventional coating method,the liquid coating composition can be diluted by the addition of anorganic solvent. Examples of such a diluent solvent include monohydricalcohols, polyhydric alcohols, ethers such as an ether of a polyhydricalcohol, carboxylic acids such as acetic and propionic acids, ketonessuch as acetone, methyl ethyl ketone, acetylacetone and methyl isobutylketone, and esters such as methyl acetate, ethyl acetate, butyl acetateand isoamyl acetate.

Besides the above described method for the preparation of the liquidcoating composition used in the inventive method, in which the first andsecond silane compounds as such are mixed together and subjected to thepartial cohydrolysis-condensation reaction, an alternative method forthe preparation of the liquid coating composition is that the secondsilane compound having at least one functional group in a molecule issubjected, prior to mixing with the first silane compound, to a partialintermolecular reaction of the functional groups or, for example, thefree-radical polymerization of the ethylenically unsaturated functionalgroups such as the vinyl, 3-acryloxypropyl and 3-methacryloxypropylgroups in an organic solvent under heating with admixture of afree-radical polymerization initiator such as tert-butyl hydroperoxide,cumene hydroperoxide, 2,2'-azobisisobutyronitrile, benzoyl peroxide,2,2'-azobis(2,4-dimethylvaleronitrile) and the like. In conducting theabove mentioned preliminary polymerization reaction of the second silanecompound prior to the cohydrolysis reaction with the first silanecompound, it is optional that the polymerization mixture is admixed witha polyfunctional acrylic monomer mentioned above so as to effectcopolymerization of the second silane compound and the polyfunctionalacrylic monomer.

In the above described procedure for the preparation of a liquid coatingcomposition used in the inventive method, the second silane compound isused in an amount in the range from 0.05 to 9 moles or, preferably, from0.1 to 5 moles per mole of the first silane compound and the amount ofwater added to the reaction mixture for the hydrolysis is in the rangefrom 2 to 10 moles or, preferably, from 3 to 8 moles per mole of thetotal amount of the first and second silane compounds. The hydrolysisreaction is promoted by the addition of an acid as a catalyst, which ispreferably an inorganic acid such as hydrochloric, nitric and phosphoricacids. The amount of the acid catalyst added to the reaction mixture ispreferably in the range from 0.001 to 0.1% by weight based on the totalamount of the first and second silane compounds. When a polyfunctionalacrylic monomer is used in several different ways described above, theamount thereof is in the range from 0.5 to 300 parts by weight per 100parts by weight of the second silane compound.

The liquid coating composition prepared from the first and second silanecompounds and, optionally, a polyfunctional acrylic monomer in the abovedescribed manner can be admixed with a finely divided inorganic fillerso that the protective coating film formed on a substrate surface bycuring the composition is imparted with further increased mechanicalstrengths or, in particular, with an increased hardness and resistanceagainst scratches. The average particle diameter of the finely dividedinorganic filler should be in the range from 5 to 200 nm. Examples ofsuitable inorganic fillers include colloidal silica, fumed silicafillers, finely divided titanium dioxide fillers, colloidal alumina andthe like. Various grades of commercial products are available on themarket for these inorganic fillers and can be used as such. They can beused either singly or as a combination of two kinds or more according toneed.

The amount of the finely divided inorganic filler, when added, in theliquid coating composition used in the inventive method is in the rangefrom 0.3 to 500 parts by weight or, preferably, from 0.5 to 200 parts byweight per 100 parts by weight of the liquid coating composition beforeadmixture of the inorganic filler. When the amount of the inorganicfiller is too small, the desired effect of improvement in the hardnessof the protective coating film cannot be obtained as a matter of coursewhile, when the amount thereof is too large, the protective film formedfrom the coating composition would be somewhat brittle and the adhesionof the protective coating film to the substrate surface is decreased. Ifnecessary, a dispersion aid can be added to the liquid coatingcomposition prepared with admixture of an inorganic filler in order toensure homogeneity and stability of dispersion.

In step (a) of the inventive method, the surface of a substrate, whichis to be protected by forming a protective coating film thereon, isuniformly coated with the liquid coating composition prepared in theabove described manner by using a suitable coating machine such as aspinner depending on the particular types of the substrate material. Thecoating amount is also dependent on the particular types of thesubstrate material but the thickness of the coating layer is usually inthe range from 0.01 to 5 μm as dried.

In step (b) of the inventive method, the coating layer of the aboveprepared liquid coating composition is dried and heated at a temperatureof 140° C. or higher or, preferably, in the range from 150° to 300° C.for a length of time in the range from 15 to 120 minutes in air toeffect full curing of the coating layer.

In the following, the method of the present invention is described inmore detail by way of examples.

EXAMPLE 1

A solution prepared by dissolving 152 g (1 mole) of tetramethoxy silaneand 248 g (1 mole) of 3-methacryloxypropyl trimethoxy silane in 175 g ofn-butyl alcohol was admixed with 126 g of deionized water and 0.02 g ofconcentrated hydrochloric acid to form a reaction mixture which wasagitated at room temperature for about 6 hours to effect partialcohydrolysis-condensation reaction of the silanes. The thus obtainedreaction mixture was diluted by the addition of 200 g of butyl acetateand 300 g of propyleneglycol monopropyl ether to give a liquid coatingcomposition.

The thus prepared liquid coating composition was uniformly applied byusing a spinner on to the surface of a 6-inch glass substrate plate, onwhich a stripe pattern of red, blue and green with a line width of 80 μmand a space width of 20 μm was formed, and the coating layer was, afterdrying, baked at 250° C. for 1 hour to give a fully cured protectivefilm having a thickness of 2.0 μm. This protective film had a pencilhardness of 7 H. In the next place, an electroconductive ITO film wasformed on the protective film by the sputtering method and anorientation membrane of a polyimide resin was formed further thereon tocomplete a display panel specimen, which was subjected to a heating testat 250° C. for 1 hour to find appearance of absolutely no creases orformation of cracks on both of the stripe pattern and the ITO film.

EXAMPLE 2

A solution prepared by dissolving 208 g (1 mole) of tetraethoxy silane,117 g (0.5 mole) of 3-acryloxypropyl trimethoxy silane and 74 g (0.5mole) of vinyl trimethoxy silane in 170 g of isopropyl alcohol wasadmixed with 190 g of deionized water and 0.02 g of concentrated nitricacid to form a reaction mixture which was agitated at room temperaturefor about 6 hours to effect partial cohydrolysis-condensation reactionof the silanes. The thus obtained reaction mixture was diluted by theaddition of 240 g of butyl acetate and 200 g of ethyleneglycol monobutylether to give a liquid coating composition.

A 6-inches glass substrate plate was provided with a protective film bycoating with the thus prepared liquid coating composition followed bydrying and baking of the coating layer in substantially the same manneras in Example 1 except that the baking treatment of the coating layerwas performed at 200° C. for 2 hours and the protective coating filmthus formed had a thickness of 1.5 μm. This protective film had a pencilhardness of 6 H. The result of the heat resistance test of the completeddisplay panel specimen undertaken under the same conditions as inExample 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 3

A solution prepared by dissolving 208 g (1 mole) of tetraethoxy silane,68.8 g (0.2 mole) of di(3-methacryloxypropyl) dimethoxy silane and 27.8g (0.1 mole) of 3-glycidyloxypropyl triethoxy silane in 90 g of isoamylacetate was admixed with 88 g of deionized water and 0.01 g ofphosphoric acid to form a reaction mixture which was agitated at roomtemperature for about 6 hours to effect partialcohydrolysis-condensation reaction of the silanes. The thus obtainedreaction mixture was diluted by the addition of 100 g of isoamyl acetateand 200 g of hexyleneglycol to give a liquid coating composition.

A 6-inches glass substrate plate was provided with a protective film bycoating with the thus prepared liquid coating composition followed bydrying and baking of the coating layer in substantially the same manneras in Example 1 except that the baking treatment of the coating layerwas performed at 160° C. for 2 hours and the protective coating filmthus formed had a thickness of 1.5 μm. This protective film had a pencilhardness of 7 H. The result of the heat resistance test of the completeddisplay panel specimen undertaken under the same conditions as inExample 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 4

A solution prepared by dissolving 46 g (0.3 mole) of tetramethoxy silaneand 278 g (1 mole) of 3-glycidyloxypropyl triethoxy silane in 100 g ofbutyl acetate was admixed with 76 g of deionized water and 0.01 g ofhydrochloric acid to form a reaction mixture which was agitated at roomtemperature for about 6 hours to effect partialcohydrolysis-condensation reaction of the silanes. The thus obtainedreaction mixture was diluted by the addition of 200 g ofdipropyleneglycol, 50 g of octyleneglycol and 73 g of butyl acetate togive a liquid coating composition.

A 6-inches glass substrate plate was provided with a protective film bycoating with the thus prepared liquid coating composition followed bydrying and baking of the coating layer in substantially the same manneras in Example 1 except that the baking treatment of the coating layerwas performed at 160° C. for 2 hours and the protective coating filmthus formed had a thickness of 1.5 μm. This protective film had a pencilhardness of 6 H. The result of the heat resistance test of the completeddisplay panel specimen undertaken under the same conditions as inExample 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 5

Into a three-necked flask of 2 liters capacity equipped with a refluxcondenser, thermometer and dropping funnel were introduced 248 g (1mole) of 3-methacryloxypropyl trimethoxy silane and 400 g ofpropyleneglycol monomethyl ether to form a reaction mixture. Thereafter,a solution of 2.5 g of 2,2'-azobisisobutyronitrile in 90 g ofethyleneglycol monomethyl ether as a polymerization initiator was addeddropwise into the reaction mixture in the flask with agitation at 60° C.under an atmosphere of nitrogen gas. After completion of the dropwiseaddition of the polymerization initiator, agitation of the reactionmixture in the flask was continued further at 80° C. for 1 hour and thenat 110° C. for additional 1 hour to complete the polymerization reactionfollowed by cooling to room temperature. In the next place, the reactionmixture in the flask was admixed with 152 g (1 mole) of tetramethoxysilane together with 126 g of deionized water and 0.02 g of concentratedhydrochloric acid and agitated at room temperature for about 6 hours toeffect partial cohydrolysis-condensation reaction of the silanes. Thethus obtained reaction mixture was diluted by the addition of 200 g ofbutyl acetate and 136 g of isopropyl alcohol to give a liquid coatingcomposition.

A 6-inches glass substrate plate was provided with a protective film bycoating with the thus prepared liquid coating composition followed bydrying and baking of the coating layer in substantially the same manneras in Example 1 except that the baking treatment of the coating layerwas performed at 200° C. for 2 hours and the protective coating filmthus formed had a thickness of 1.5 μm. This protective film had a pencilhardness of 6 H. The result of the heat resistance test of the completeddisplay panel specimen undertaken under the same conditions as inExample 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 6

The experimental procedure was substantially the same as in Example 5described above except that, instead of the preliminaryhomopolymerization of 3-methacryloxypropyl trimethoxy silane,copolymerization was performed in a polymerization mixture prepared bydissolving 248 g (1 mole) of 3-methacryloxypropyl trimethoxy silane and6 g (0.02 mole) of pentaerithritol trimethacrylate in 400 g ofpropyleneglycol monomethyl ether.

A 6-inches glass substrate plate was provided with a protective film bycoating with the thus prepared liquid coating composition followed bydrying and baking of the coating layer in substantially the same manneras in Example 1 except that the baking treatment of the coating layerwas performed at 200° C. for 2 hours and the protective coating filmthus formed had a thickness of 1.5 μm. This protective film had a pencilhardness of 6 H. The result of the heat resistance test of the completeddisplay panel specimen undertaken under the same conditions as inExample 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 7

The experimental procedure was substantially the same as in Example 1except that the liquid coating composition was further admixed with 6 g(0.06 mole) of dipentaerithritol hexaacrylate, the protective coatingfilm had a thickness of 1.5 μm and the baking treatment of the coatinglayer was performed at 200° C. for 2 hours. The protective film had apencil hardness of 6 H. The result of the heat resistance test of thecompleted display panel specimen undertaken under the same conditions asin Example 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

EXAMPLE 8

The experimental procedure was substantially the same as in Example 1except that the liquid coating composition was further admixed with 60 g(0.06 mole) of hexa(2-acryloxyethyl) phosphazene, the protective coatingfilm had a thickness of 1.5 μm and the baking treatment of the coatinglayer was performed at 200° C. for 2 hours. The protective film had apencil hardness of 6 H. The result of the heat resistance test of thecompleted display panel specimen undertaken under the same conditions asin Example 1 was that the specimen was fully heat-resistant to causeabsolutely no creases or crack formation.

COMPARATIVE EXAMPLE 1

The experimental procedure was about the same as in Example 1 exceptthat the liquid coating composition here used was a solution prepared bydissolving 5 g of a soluble polyimide resin in 95 g ofN-methyl-2-pyrrolidone and the baking treatment of the coating layer wasperformed at 200° C. for 2 hours to give a protective film having athickness of 1.5 μm of which the pencil hardness was 2 H. The result ofthe heat-resistance test of the completed display panel specimen wasthat creases were found in both of the stripe pattern and the ITOmembrane.

COMPARATIVE EXAMPLE 2

The experimental procedure was about the same as in Example 1 exceptthat the liquid coating composition here used was prepared by dissolving30 g of a clear epoxy resin (Epikote 1004, a product by Yuka Shell Co.)in 70 g of ethyleneglycol monobutyl ether and the baking treatment ofthe coating layer was performed at 200° C. for 2 hours to give aprotective film having a thickness of 1.5 μm of which the pencilhardness was 2 H. The result of the heat-resistance test of thecompleted display panel specimen was that creases were found in both ofthe stripe pattern and the ITO membrane.

EXAMPLE 9

A solution prepared by dissolving 152 g (1 mole) of tetramethoxy silaneand 248 g (1 mole) of 3-methacryloxypropyl trimethoxy silane in 175 g ofn-butyl alcohol was admixed with 126 g of deionized water and 0.02 g ofconcentrated hydrochloric acid and agitated at room temperature forabout 6 hours to effect partial cohydrolysis-condensation reaction ofthe silanes. Thereafter, a 70 g portion of the thus obtained reactionmixture was admixed with a colloidal silica having a particle diameterof 10 to 20 nm (Snowtex, a product by Nissan Chemical Co.) in an amountof 228 g as solid, 10 g of n-butyl acetate and 395 g of propyleneglycolmonopropyl ether to give a liquid coating composition.

A 6-inches substrate plate of glass provided with an electrode patternof ITO film having a line width of 80 μm was uniformly coated by using aspinner with the above prepared liquid coating composition to form acoating layer which was dried and subjected to a baking treatment at250° C. for 1 hour to give a cured protective film having a thickness of100 nm and a pencil hardness of 9 H. The protective film was veryuniform over the whole area absolutely without cracks.

EXAMPLE 10

A solution prepared by dissolving 208 g (1 mole) of tetraethoxy silane,117 g (0.5 mole) of 3-acryloxypropyl trimethoxy silane and 74 g (0.5mole) of vinyl trimethoxy silane in 170 g of isopropyl alcohol wasadmixed with 190 g of deionized water and 0.02 g of concentrated nitricacid and agitated at room temperature for about 6 hours to effectpartial cohydrolysis-condensation reaction of the silanes. Thereafter,the thus obtained reaction mixture was admixed with 6.35 g of a finelydivided silica powder having an average particle diameter of 100 nm(Hipresica FQ, a product by Ube-Nitto Chemical Co.), 100 g of isopropylacetate and 403.5 g of ethyleneglycol monomethyl ether to give a liquidcoating composition.

A cured protective film having a thickness of 100 nm was formed usingthe thus prepared liquid coating composition on a glass substrate platein the same manner as in Example 9 except that the baking treatment wasperformed at a temperature of 200° C. for 2 hours. The protective filmwas very uniform over the whole area and had a pencil hardness of 8 H.

EXAMPLE 11

A solution prepared by dissolving 208 g (1 mole) of tetraethoxy silane,27.8 g (0.1 mole) of 3-glycidyloxypropyl triethoxy silane and 68.8 g(0.2 mole) of di(3-methacryloxypropyl) dimethoxy silane in 90 g ofethyleneglycol monoethyl ether was admixed with a colloidal silicahaving a particle diameter of 10 to 20 nm (Adelite AT, a product byAsahi Denka Kogyo Co.) in an amount of 60 g as solid and a colloidalalumina having a particle diameter of 10 to 20 nm (Snowtex AS, a productby Nissan Chemical Co.) in an amount of 18 g as solid in combinationfollowed by the addition of 88 g of deionized water and 0.01 g ofphosphoric acid and agitated at room temperature for about 6 hours toeffect partial cohydrolysis-condensation reaction of the silanes.Thereafter, the thus obtained reaction mixture was diluted by theaddition of 100 g of dipropyleneglycol monomethyl ether, 100 g ofisoamyl acetate and 200 g of hexyleneglycol to give a liquid coatingcomposition.

A cured protective film having a thickness of 180 nm was formed usingthe thus prepared liquid coating composition on a glass substrate platein the same manner as in Example 9 except that the baking treatment wasperformed at a temperature of 160° C. for 2 hours. The protective filmwas very uniform over the whole area and had a pencil hardness of 9 H.

EXAMPLE 12

A solution prepared by dissolving 46 g (0.3 mole) of tetramethoxy silaneand 278 g (1 mole) of 3-glycidyloxypropyl triethoxy silane in 100 g ofbutyl acetate was admixed with 76 g of deionized water and 0.01 g ofconcentrated hydrochloric acid and agitated at room temperature forabout 6 hours to effect partial cohydrolysis-condensation reaction ofthe silanes. Thereafter, the thus obtained reaction mixture was admixedwith a finely divided titanium dioxide powder having an average particlediameter of 17 nm (Idemitsu Titania, a product by Idemitsu Kosan Co.) inan amount of 33 g as solid and diluted by the addition of 300 g ofisopropyl alcohol, 200 g of dipropyleneglycol, 50 g of octyleneglycoland 73 g of isobutyl acetate to give a liquid coating composition.

A cured protective film having a thickness of 200 nm was formed usingthe thus prepared liquid coating composition on a glass substrate platein the same manner as in Example 9 except that the baking treatment wasperformed at a temperature of 160° C. for 2 hours. The protective filmwas very uniform over the whole area and had a pencil hardness of 9 H.EXAMPLE 13

Into a three-necked flask of 2 liters capacity equipped with a refluxcondenser, thermometer and dropping funnel were introduced 248 g (1mole) of 3-methacryloxypropyl trimethoxy silane and 400 g ofpropyleneglycol monomethyl ether to form a reaction mixture, into whicha solution of 2.5 g of 2,2'-azobisisobutyronitrile in 90 g ofethyleneglycol monoethyl ether was added dropwise at 60° C. withagitation under an atmosphere of nitrogen and agitation was continuedthereafter for 1 hour at 80° C. and then for 1 hour at 110° C. to effectpolymerization of the silane compound followed by cooling to roomtemperature. Thereafter, the thus obtained reaction mixture was admixedwith 152 g (1 mole) of tetramethoxy silane together with 126 g ofdeionized water and 0.02 g of concentrated hydrochloric acid andagitated at room temperature for about 6 hours to effect partialcohydrolysis-condensation reaction of the silane compounds. Thereafter,a 100 g portion of the thus obtained reaction mixture was admixed with acolloidal silica having a particle diameter of 10 to 20 nm (Snowtex, aproduct by Nissan Chemical Co.) in an amount 228 g as solid, 20 g ofn-butyl acetate, 13 g of isopropyl alcohol and 340 g of propyleneglycolmonopropyl ether to give a liquid coating composition.

A cured protective film having a thickness of 120 nm was formed usingthe thus prepared liquid coating composition on a glass substrate platein the same manner as in Example 9 except that the baking treatment wasperformed at a temperature of 200° C. for 2 hours. The protective filmwas very uniform over the whole area and had a pencil hardness of 9 H.

EXAMPLE 14

The experimental procedure was substantially the same as in Example 13except that the polymerization of 1 mole of 3-methacryloxypropyltrimethoxy silane in 400 g of propyleneglycol monomethyl ether wasperformed with further addition of 6 g (0.02 mole) of pentaerithritoltrimethacrylate as a comonomer to the reaction mixture.

A cured protective film having a thickness of 150 nm was formed usingthe liquid coating composition prepared with the above describedmodification of the procedure on a glass substrate plate in the samemanner as in Example 9 except that the baking treatment was performed ata temperature of 200° C. for 2 hours. The protective film was veryuniform over the whole area and had a pencil hardness of 9 H.

EXAMPLE 15

The experimental procedure was substantially the same as in Example 9except that the liquid coating composition prepared in the same mannerwas further admixed with 6 g (0.01 mole) of dipentaerithritolhexaacrylate.

A cured protective film having a thickness of 180 nm was formed usingthe liquid coating composition prepared with the above describedmodification on a glass substrate plate in the same manner as in Example9 except that the baking treatment was performed at a temperature of200° C. for 2 hours. The protective film was very uniform over the wholearea and had a pencil hardness of 9 H.

EXAMPLE 16

The experimental procedure was substantially the same as in Example 9except that the liquid coating composition prepared in the same mannerwas further admixed with 60 g (0.06 mole) of hexa(2-acryloxyethyl)phosphazene.

A cured protective film having a thickness of 150 nm was formed usingthe liquid coating composition prepared with the above describedmodification on a glass substrate plate in the same manner as in Example9 except that the baking treatment was performed at a temperature of200° C. for 2 hours. The protective film was very uniform over the wholearea and had a pencil hardness of 9 H.

What is claimed is:
 1. A method for the formation of a protectivecoating film on the surface of a substrate which comprises the stepsof:(a) coating the surface with a liquid coating composition containinga partial cohydrolysis-condensation product of a silane mixtureconsisting essentially of first silane compound represented by theformula:

    Si(OR).sub.4,

in which R is an alkyl group having 1 to 4 carbon atoms or a phenylgroup, and a second silane compound represented by the formula:

    R.sup.1.sub.n Si(OR).sub.4-n,

in which R has the same meaning as defined above, R¹ is a functionalgroup which is a polymerizable group selected from the group consistingof vinyl, 3-acryloxypropyl and 3-methacryloxypropyl and3-glycidyloxypropyl and n is 1, 2 or 3, to form a coating layer, andwherein the amount of the second silane compound is in the range from0.05 to 9 moles per mole of the first silane compound; and (b) dryingand heating the coating layer at a temperature in the range from 140° to300° C. for 15 to 120 minutes.
 2. The method for the formation of theprotective coating film on the surface of the substrate as claimed inclaim 1 in which the liquid coating composition further contains apolyfunctional acrylic monomer in an amount in the range from 0.5 to 300parts by weight per 100 parts by weight of the second silane compound.3. The method for the formation of the protective coating film on thesurface of the substrate as claimed in claim 1 in which the liquidcoating composition further contains a finely divided inorganic fillerhaving an average particle diameter in the range of 5 to 200 nm.
 4. Amethod for the formation of a protective coating film on the surface ofa substrate which comprises the steps of:(a) coating the surface with aliquid coating composition containing a partiallycohydrolysis-condensation product of a silane mixture consistingessentially of first silane compound represented by the formula:

    Si(OR).sub.4,

in which R is an alkyl group having 1 to 4 carbon atoms or a phenylgroup, and an intermolecular reaction product of a second silanecompound represented by the formula:

    R.sup.1.sub.n Si(OR).sub.4-n,

in which R has the same meaning as defined above, R¹ is a functionalgroup which is a polymerizable group selected from the group consistingof vinyl, 3-acryloxypropyl and 3-methacryloxypropyl and3-glycidyloxypropyl and n is 1, 2 or 3, to form a coating layer, andwherein the amount of the second silane compound is in the range from0.05 to 9 moles per mole of the first silane compound; and (b) dryingand heating the coating layer at a temperature in the range from 140° to300° C. for 15 to 120 minutes.
 5. The method for the formation of theprotective coating film on the surface of the substrate as claimed inclaim 4 in which the functional group in the second silane compound is apolymerizable group and the intermolecular reaction product of thesecond silane compound is a polymerization product thereof.
 6. Themethod for the formation of the protective coating film on the surfaceof the substrate as claimed in claim 4 in which the liquid coatingcomposition further contains a polyfunctional acrylic monomer in anamount in the range from 0.5 to 300 parts by weight per 100 parts byweight of the second silane compound.
 7. The method for the formation ofthe protective coating film on the surface of the substrate as claimedin claim 4 in which the liquid coating composition further contains afinely divided inorganic filler having an average particle diameter of 5to 200 nm.